1. Field of the Invention
The present invention relates to a novel thermoplastic, biodegradable hydrogel copolymers. More specifically, this invention concerns the bioabsorbable copolymers used for medical applications according to the biodegradable property of polyethyleneoxide(PEO) in a block copolymer essentially consisting of PEO, polylactide(PLA) and polyglycolide(PGA).
2. Description of the Prior Art
Recently, hydrogels have been used widely in a variety of biochemical applications, for example, contact lenses, burn dressings, implants, lubricant coatings and drug delivery devices.
In some of these areas, crosslinked hydrogel materials have met with great success. However, these materials suffer drawbacks, such as a lack of processibility as a consequence of their cross-linked nature.
To minimize these problems, the use of block copolymer having thermoplastic and biodegradable properties has been researched. Particularly, the research focused to ABA type triblock copolymer has proceeded positively.
An ABA triblock copolymer, the middle block(B) as polyethyleneoxide having a hydrophilic property and the end blocks(A) as polylactide, polyglycolide or their copolymer having hydrophobic and biodegradable properties, was reported by J. of Bio. Mat. Res. Vol 21, 1301(1987) and J. of poly. Sci. Part A, Polymer Chemistry, Vol. 27, 2151(1989). Other block copolymers synthesized by hydrophilic and hydrophobic polymers were disclosed by U.S. Pat. Nos. 4,942,035 and 4,716,203. Among these block copolymers, polylactide has been chiefly used as hydrophobic polymer and polyethyleneoxide has been generally used as hydrophilic polymer due to its safety to the human body.
The above mentioned patents disclosed the triblock copolymers as a shape of PLA/PEO/PLA, in which PEO shows hydrophilic property and PLA shows hydrophobic property. Furthermore, the molecular weight of PEO in these patents has to be more than 8,000, particularly, PEO M.W. 8,000, PEO M.W. 14, 000 and PEO M.W. 20, 000, in order to sustain the hydrophilic property of whole triblock copolymer.
However, the PEO more than M.W. 4,000 is very hard to use for medical application, since it hardly excretes through the human kidney.